Telementering system



Sept. 21, 1954 J. F. KALBACH ETAL 2,689,949

TELEMETERING SYSTEM Filed May 15, 1952 13 Sheets-Sheet 1 ins frum en 1'0 fion A 5/3 em b/y Decoder and Transm/f fer De fee for L igh 1 Pulse L lgn 1 Pulse Receiver E mil-fer I l I l l Llgln Pulse FJ L/gn f Pulse Emlffer Receiver 7 A V 29 neon ERA ran BU/L nnve 6'0 TROL ROOM v 27-; 25 '1 I Channel Decoder I and Defeefor A v Gen frel Roam Console Fig.

WITNESSES: INVENTORS Jolm E Kalbeel:

W Har BYO/mrlee Wllkln Jannsfane Sept. 21, 1954 J. F. KALBACH ETAL TELEMETERING SYSTEM 13 Sheets-Sheet 2 Filed May 15, 1952 TRANSMITTER Trigger Genera for Ligh f Emifver cum/f INVENTORS: John E Ka/bach Char/es Wi/k/h BY WITNESSES.

Johnstone Sept. 21, 1954 J. F. KALBACH ETAL TELEMETERING SYSTEM Filed May 15, 1952 7 l3 Sheets-Sheet 3 400 ,asec

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INVENTORS John E Ka/buch WITNESSES BYG/lqr/es Wi/kin Johnsfone Sept. 21, 1954 J. F. KALBACH ETAL TELEMETERING SYSTEM 15 Sheets-Sheet 4 Filed May 15, 1952 Mixer Coder Y 7'0 Ofhar Madu/afor Circa/f5 Timer INVENTORS John E Ka/bac/r WITNESSES Ghar/es Wf/k/n da/msfone BY fl w/4M J F. KALBACH ETAL 2,689,949

TELEMETERING SYSTEM 13 Sheets-Sheet 6 INVENTORS John F. Ka/bac/z YGhar/es Wi/k/n .Jabnsfane B Sept. 21, 1954 Filed May 15, 1952 70 Of/wr Flip-Flop Circa/is WITNESSES Sept. 21, 1954 J. F. KALBACH ETAL TELEMETERING SYSTEM 13 Sheets-Sheet 7 Filed May 15, 1952 INVENTORS: John E Ka/bac/I W/ TIVESSES Char/es Wi/lrin Jo/msfane BY 4 Sept. 21, 1954 J. F. KALBACH ETAL 2,639,949

TELEMETERING SYSTEM Filed May 15, 1952 13 Sheets-Sheet 8 0 Delayed 8 lnverfed A 8 6 D lnverfed Normal 8 Delayed Normal mal WITNESSES INVENTORS Jo/m E Ka/bach 1% w BYG/mr/es Wi/k/n Johnsfane 55 7 A 444.

Sept. 21, 1954 J. F. KALBACH ETAL TELEMETERING SYSTEM 15 Shee ts-Sheet 9 Filed May 15. 1952 Differs/r fin fad INVENTORS John E Kfl/bGC/I WITNESSES:

Char/es W/'/k/'/7 Johnsfone BY Sept. 21, 1954 J. F. KALBACH ET AL 2,689,949

TELEMETERING SYSTEM Filed May 15, 1952 15 Sheets-Sheet 10 Sfopp/ng Pulse +250 Vo/fs Tune 70 Repefif/on Frequency 500 0.0. Oufpuf .OI zf 0 Vol fs WITNESSES: INVENTORS John E Ka/bac/z W BYC/mr/es Wf/k/n Jo/msfone P 1954 .1. F. KALBACH ET AL 2,689,949

TELEMETERING SYSTEM Filed May 15, 1952 13 Sheets-Sheet 12 Mefer A 7 Decoder 9 5 Defecfar Fig. /7 I U M WITNESSES IN VEN TORS John E Ka/bac/l Ma Wm ByC/mr/es Wi/k/n Johnsfone Patented Sept. 21, 1954 UNITED STATES PATENT OFFICE TELEMETERING SYSTEM Commission Application May 15, 1952, Serial No. 287,876

18 Claims.

This invention relates to communication systems and, more particularly, to multi-signal telemetering systems.

It is a frequent occurrence in the practical operation of machinery that certain functions of the machinery must be observed and controlled from a remote location. Very high voltage generating machinery, such as Van de Graaff generators, fall within this category and impose additional problems because of the presence of exceedingly high voltages.

The present invention concerns itself with a multi-function telemetering system for controlling and observing a large number of items in the high voltage electrode, It is stressed, however, that this telemetering system is not necessarily limited to the herein described application to a Van de Graafi' generator, but is applicable to the observation and control of remotely located apparatus or machinery of any description.

The number of items to be controlled or observed in the case of a Van de Graaii generator are more than sixteen. Consequently, although other applications for a telemetering system may involve more or less items, the present explanation is directed to a four channel system capable of carrying more than sixteen different signals. Further, the exceedingly high voltage nature of the Van de Graafi generator application prohibits the use of wired links; and the presence of static discharges prohibits the successful use of electromagnetic Waves of the radio frequency type. Consequently, the system herein described utilizes light beam transmission although it is to be understood that other applications of the invention may utilize any known system of transmission. In any case, only one carrier medium in each direction between the observation or control room and the machinery is utilized. This requires the time-sharing of the carrier medium by a plurality of different signals. In order that the signals between the transmitting and receiving equipment will, under no circumstances, become out of synchronism, a coded channel system is needed.

Accordingly, it is an object of this invention to provide a telemetering system which communicates a plurality of items of information with complete reliability.

It is anoth r object of this invention to provide a system of multi-signal communication which utilizes only one carrier in each direction.

Still another object is to provide a telemetering system which utilizes a light beam link between the transmitter and receiver.

Another object is to provide a telemetering system which effects high voltage isolation.

Still another object is to provide a telemetering system which has no susceptibility to interference from electric flash-overs.

Another object of the invention is to provide a communication system having a plurality of channels each of which has a distinctive code of impulses.

Another object of this invention is to provide a communication system in which intelligence quantities are proportional to the duration between the channel identifying code and a signal impulse.

Still another object of the invention is to provide a telemetering system comprising a plurality of channels arranged to transmit both constant and alternating quantities simultaneously in said channels.

Still another object is the provision of a novel multiplexing system in which a plurality of direct current quantities can be communicated in the space allotted to any one signal in any channel.

These and other objects will become apparent from the following description taken with reference to the drawings which are made a part of this specification.

The figures of the drawing are brieflyas follows:

Figure 1 is a diagrammatic showing of the telemetering system of this invention as utilized in a Van de Graaff installation;

Figure 2 is a block diagrammatic representation of a single channel system presented for purposes of explanation;

Figure 3 is a chart showing the channel identiiying coding pulses in a four-channel multiple signal system;

Figure 4 is a chart showing the channel identification coding pulses and the time space allotted to the signal pulses;

Figure 5 is a chart showing the identification of four channels and four signals in each channel;

Figure 6 is a block diagram in part of the telemetering transmitter;

Figure 7 is a block diagram in part of the tele metering receiver showing the channel identitying decoding components;

Figure 8 is a block diagram in part of the telemetering system showing the signal decoding components;

Figure 9 is a schematic diagram in part of a preferred embodiment of the transmitter;

Figure 10 is a schematic diagram in part of the receiver;

Figure 11 is a chart showing the electronic behavior of a component;

Figure 12 is a chart showing how alternating current and direct current signals are transmitted simultaneously;

Figure 13 is a second chart useful in explaining the mode of simultaneously transmitting A. C. signals along with a D. C. signal;

Figure 14 is a schematic of a detector for use when only A. C. signals are transmitted;

Figure 15 is a block diagram showing the mode of connections for transmitting several A. C. or D. C. or A. C. and D. C. signals in the channel time space alloted to one signal;

Figure 16 is a schematic diagram showing a transmitter time-sharing system for two direct current signals;

Figure 17 is a schematic diagram of a portion of the time-shared rectifier in the receiver, and

Figure 18 is a schematic of an actual timeshared rectifier in the receiver.

The major components of the telemetering system and their relation one to another are described With reference to Figure l.

The transmission in the direction from the Van de Graaff to the control room utilizes a transmitter 22 having a light beam emitter 23 supported at the high voltage head of the Van de Graaif generator 2|. A light-sensitive receiver 24 is supported in the light beam path at the foot of the Van de Graafi generator. A transmission line 29 connects the receiver to a channel decoder and detector 25 which is connected to appropriate instruments on the control room console 26.

The motive power for the electronic equipment and controls positioned at the high voltage head is provided by a generator 32 driven off the upper Van de Graaff belt trunnion.

The telemetering system in the reverse direction is essentially the same as described in the preceding paragraphs except that somewhat different modulation techniques may be utilized in order to manipulate devices at the head of the Van de Graaif generator from the control room.

Specifically, transmitter 21 generates pulses corresponding to intelligence derived from control room console 26; the pulses are impressed on light emitter 28; the light is beamed to light pulse receiver 30, the intelligence is decoded in decoderdetector 3| and is utilized in the instrumentation assembly 19.

The understanding of the multi-signal system will be facilitated by a brief description of the principles of this invention applied to a singlechannel system. This simplified system is shown in Figure 2.

Two types of pulses are the minimum required for a single-channel system. These types are channel coding trigger pulses and delayed or signal pulses, repeated alternately at a selected repetition rate. The two pulses must be distinguishable in some way, as for example, by different amplitudes or widths, or as shown in Figure 2, by opposite polarity. The interval or delay between the two pulses is a function of an observed quantity Which may be a voltage.

In order to distinguish between those pulses which initiate time durations and those pulses which terminate durations measured from the former, the former pulses are termed channel 4 coding pulses and the latter are termed signal pulses.

The transmitter 22 comprises a trigger generator 36; a modulator 37, a delay system 3d, and a light emitter 23. The trigger generator 36 generates a pulse at even intervals. These pulses are fed both to the light emitter 2B and to the delay system 33. The delay system operates to delay each signal pulse for an interval of time depending on the signal voltage impressed on modulator unit 31. The time interval between each original pulse and the corresponding delayed pulse is accordingly a function of the amplitude of the intelligence to be transmitted. The two sets of pulses are impressed on light emitter 2t and transmitted as intensified or diminished variations from the normal intensity of the light emitted. The relation of the channel identifying pulses and the delayed pulses is explained, infra, and is shown in the chart to the right of the light emitter. For brevity, these variations in intensity are henceforth termed positive or negative light pulses.

After transmission over the modulated light beam, the pulses are received in light-sensitive receiver 2 amplified, separated and used to control a flip-flop circuit il in such a way that a square Wave of voltage is generated whose duration corresponds to the duration between each original channel pulse and each signal pulse. The square wave pulses are applied to a sawtooth wave generator #312 so that sawtooth voltages having an amplitude corresponding to the length of the square waves are generated. The sawtooth potentials are rectified in peak detector t3. An output is obtained which is a relatively steady voltage which will have an amplitude corresponding to the input or modulating votlage applied to modulator 3'? in the transmitter.

The voltage impulse charts to the right of the equipment components in Figure 2 serve to explain the mode of operation. Trigger generator 36 generates negative pulses h at even intervals as shown in chart H. These pulses are also applied to delay component 38 wherein they are delayed for intervals depending on the amplitude of the modulating potential generated in modulator 3? and the modulating potential, in turn, is a function of the value of the observed input potentials identified as V1 and V2. That is, a potential V2 of greater amplitude than V1 causes a proportionally greater delay as shown by z" compared to i in chart 1. Both the original pulses and the delayed pulses are combined, as shown in chart J, and are applied to light emitter 23 to be transmitted over the light beam to the light-sensitive receiver 26. The initial or channel identifying pulses are used to start flip-flop circuit ii and the delayed or signal pulses are used to return the flip-flop circuit to its original state. It follows that the length of the square wave from the flipfiop circuit is a function or" the delay time between an original pulse and the corresponding delayed pulse. The length of the square wave is shown in chart K and is equal to 1 or 2 which, in turn, corresponds to V1 or V2. The flip-flop circuit starts and stops a sawtooth generator 42. The sawtooth wave has an amplitude corresponding to the length of the square wave and the amplitude is shown as V 1 or V 2 in chart L. The sawtooth wave is pea-l: rectified to give an output voltage V 1 or V 2 which corresponds to the original input potentials V1 or V2.

In order to expand the principle of the simple system to a system for carrying a larger number of pieces of information over a single light beam, means must be employed which will channelize or identify each of the pieces of information at the receiving end. In addition, because misinformation due to failure of synchronism cannot be tolerated, a simple progressive or sequence system is not satisfactory.

The present invention obviates any possibility of cross channelizing by th use of four distinct channel identifying pulse codes which are shown in Figure 3. The particular sequence of the various codes is a matter of choice, but for purposes of explanation, the first, second, third and fourth channels are identified by a pair of positive pulses; a pair of negative pulses; a positive pulse followed by a negative pulse, and a negative pulse followed by a positive pulse, respeotively. These channel-identifying code pairs are separated by regular intervals during which the information or signal pulses are presented. The information pulses following each identifying code pulse pair are identified by the letters A, B,

C or D with an appropriate channel identifying prefix as shown in Figures 4 and 5. The signal pulses are alternately positive and negative, and for reasons to become apparent later, the delay times of pulses of the same polarity in a given group are sufficiently different one from another to be separately distinguished by flip-flop circuits having different resolving times.

The pulses emitted from the transmitter by the glow tube emitter have a duration of about 2 microseconds in the preferred embodiment. The spacing of the two pulses in each code pair is 3 microseconds. The time duration between channel code pairs is 100 microseconds.

It is understood that the duration given to any of the pulses and the interval between pulses is a matter of selection depending on the trafic for which any particular system is designed. For simplicity in explanation and as an aid in the practical application of this invention, values are herein given to time durations utilized in the selected embodiment.

The four channels are delineated by the four code pairs and each channel is utilized to handle at least four signals. The entire cycle of four code pairs and the plurality of signals is repeated 2500 times per second.

In order to keep a clear separation between signals, the time relationships shown in Figure 4 are preferably maintained. Each signal pulse is allowed a ratio of maximum to minimum delay time of about 1.5 to 1, measured from the first pulse of the corresponding code pair. The pulse occurrence area and pulse exclusion areas are shown diagrammatically. An example of actual timing of the pulses is shown and it is to be noticed that the signal pulses are excluded from a region in the center of the time spacing allotted to two signals. Preferably, the pulse exclusion regions are chosen so that if signal and code pulses vary in timing by 2 per cent, pulses other than those in the code pairs can never be closer than 5 microseconds. Consequently, this eliminates or prevents false code pairs which would disrupt the proper decoding sequence.

The actual mode of operation of the four channel transmitter-receiver system is now described with reference to Figures 6 and '7.

The transmitter The transmitter 22 comprises a timer 53 which cyclically generates four pulses of like polarity, each on a separate output terminal as shown in chart N. The pulses are applied to a coder 5! which, in a manner presently to be described. converts the four original pulses into four different code pairs as shown in chart 0.

In order for intelligence to be transmitted, signal pulses must be inserted after the first pulse of each corresponding channel coding pair with a time spacing therebetween which corresponds to the quantity to be communicated. This is accomplished in the first channel by applying the first pulse from the timer at to each of four time modulating delay units IA, [3, IC and ID. This terminology means that four signals are being processed in channel I, that is, in the interval between the first and second code pair. The modulating delay units are so arranged internally that a signal following the code pair has the selected polarity and occurs after a duration following the first pulse of the code pair which corresponds to the signal amplitude impressed thereon. For example, signal IA occurs after the first pulse of code pair I with a delay time corresponding to the amplitude of the signal derived from modulator input ill I. Signal B in the channel identified by code I follows the first pulse of code pair I after a duration corresponding to the amplitude of the signal applied on modulating delay unit EB, etc. The mixer circuit 56 is such that it is preferable to apply signal pulses to it with negative polarity, as shown in charts Q and R. The signal pulses from IA and IC modulating delay units are reversed in polarity in the mixer 56 so that these signals are emitted as positive pulses, whereas, the IE and ID pulses continue to be negative as shown in chart P.

Figure 6 shows, in addition to all the components entering into the operation of channel I, the modulating delay units 2A, 2B, 2C and 2D in channel II. It is to be noted that the timing pulse for channel II is the second pulse emitted by the timer, that is, it is the pulse shown on line 2 of chart N.

The same type of arrangement is provided for channels III and IV by the provision of the same system of components.

The channel-identifying code pairs and the signal pulses are impressed on a lamp which then transmits the channel code pulses and signal pulses in sequence as light intensity pulses.

The receiver The operation of the receiver and channel decoder detector is described with reference to Figure '7. The decoding process is explained with respect to channel I and it is to be understood that the process is similar for all channels.

The light beam impinges on photomultiplier receiver 25 and the electric potentials so derived are amplified in the two-stage amplifier SI. The combined channel code pulses and signal pulses are reproduced by the amplifier in original form as shown in chart S. These pulses are impressed on below cut-off biased stage 62 and appear in inverted form in the output as shown in chart U.

channel coding pulses are not in usable form at this stage and are simply surplus.

The signal pulses are utilized to mark the end of each corresponding duration. Accordingly, the pulses necessary to start each respective duration are yet to be derived.

The starting pulses are the channel coding pulses. It is recalled that the four channel coding pulses in the preferred embodiment are a pair of positive pulses, a pair of negative pulses, a positive followed by a negative pulse, and a negative followed by a positive pulse, respectively. The pulses of each pair are separated by a fixed delay period which is 3 microseconds in the preferred embodiment.

It follows that if the first pulse of the first channel code pair is delayed 3 microseconds by a delay network and is impressed with positive polarity on one grid of a coincidence tube at thesame time that the second pulse of the first channel code pair is directly applied with positive polarity to a second grid of the same coincidence tube, the coincidence tube will generate a pulse corresponding in time to the second pulse of the first channel code pair.

For a clear explanation of how the channel coding pulses are separated and reproduced in usable form, reference is made to Figure '7.

The cut-oil stages 52 and 8d reproduce the signal stop pulses. The channel code pulses are reproduced by coincidence circuits t5, '66, El and 68. Each coincidence circuit has a tube biased to cut-off by the action of two grids. Therefore, a separate positive pulse must be applied to each of the two grids simultaneously in order for the coincidence tube to conduct and generate one output pulse.

The pulses derived directly from amplifier 8! are applied directly to one grid of the coincidence tube in coincidence circuit 65. The form of channel coding pulses derived from amplifier as is as shown in chart W. The pulses from amplifier 6! are also applied to delay circuit 39 and emerge therefrom with a 3 microsecond delay. The positions of these pulses are indicated in chart X by sufiixes applied to the respective channel pulse code identifictaion numbers. Since the original time spacing between each pair of channel coding pulses is the same as the time delay applied to the pulses in the delay network 59, it follows that there is coincidence between the second pulse of each pair of the original pulses and the first pulse of each pair of the delayed pulses. Consequently, only one output pulse can be obtained from coincidence circuit 65. By inspection of charts W and X, coincidence of positive pulses occurs. only between channel code pulses I and I1. Channel code pulses II and II1 are negative so cannot activate the coincidence circuit 65. Channel code pulses III and I111 give one negative pulse simultaneously with one positive pulse, and channel code pulses IV and IV1 give one positive pulse coincident with one negative pulse. Therefore, coincidence circuit 65 can only give a starting pulse I corresponding to channel coding pulse I, but delayed 3 microsecends.

The manner in which the second identifying channel code pair II is decoded is explained with reference to charts Y and Z. The channel pairs shown in chart Y are derived from the input amplifier GI and inverter 63. Consequently, these code pulses have an identical time relation with the chart W group, but are inverted with respect thereto. The pulses in chart Z are derived from delay component 69 and inverter 10 so that they are delayed and inverted. Comparison between charts Y and Z shows that no coincident positive pulses occur corresponding to code pair I, but

that there is coincidence between the second positive pulse of code pair II in chart Y and the first positive pulse of the delayed pulses of group II in chart Z. No coincident positive pulses occur for coding groups III and IV in the Y-Z chart combination. Consequently, an output pulse is derived only from the second coding group II, but delayed 3 microseconds from the first pulse thereof.

The third coding group is derived from coincidence circuit 67. The input pulses are a. set of inverted pulses, as shown in chart Y, and a set of normal delayed pulses, as shown in chart X. The only pair of coincident positive pulses occur in group III. Consequently, coincidence circuit 571 delivers a single output pulse corresponding to channel code group III, but delayed 3 microseconds.

The fourth output code pulse is delivered by coincidence circuit 68 by the application thereto of one set of normal pulses, as shown in chart W, and one set of delayed and inverted pulses, as shown in chart Z. The only coincidence of positive pulses occurs in group IV.

As a result of the reproduction of the signal pulses and the channel timing pulses, a group of flip-flop circuits, one for each signal pulse, can be operated. The operation of the flip-flop circuits is shown in Figure 8.

In Figure 8, the decoder ti? includes in block form all the components of Figure 7 less the light receiver 26 and the two-stage amplifier BI.

For ease in explanation, only the operation of channels I and II is shown and discussed. The operation of the remaining channels follows from an extension of the same principles. The output pulse of coincidence circuit 65 (Figure '7) for group I is the starting pulse for actuating four flip-flop circuits marked IA, IB', lC' and iD'. Flip-flop circuit VA has a resolution time which permits it to be returned to its original state by the time the A signal pulse occurs. Flip-flop circuits I'B', IC and I'D have progressively longer resolving times than IA and so are unaffected by signal pulse A. Flipfiop circuit I'B can respond to the B signal pulse, whereas, flip-flops 1'0 and I'D cannot. In corresponding order, flip-flop circuit I'C" responds to signal pulse C and flip-flop circuit I'D responds to signal pulse D.

It is seen from the above discussion and the showing of Figure 8 that the respective decoded channel coding pulse flips all the flip-flop circuits in that channel, and each decoded signal pulse returns its corresponding flip-flop circuit to its original state. Therefore, a rectangular pulse is generated corresponding to the duration between the second of each original pair of the channel coding pulses and a signal pulse.

Each flip-flop circuit is connected to a sawtooth generator of the so-called bootstrap type. Thus, the peak value of the sawtooth potential so generated is linearly proportional to the length of the rectangular wave. The sawtooth generator is connected to a peak rectifier which delivers a steady state D. C. potential corresponding to the sawtooth peak value. A D. C. panel meter is connected to the peak rectifier. Conventional calibrating expedients are utilized to standardize each corresponding D. C. panel meter with the D. C. potential applied to the modulator at the transmitting end.

The operation of the telemetering system of this invention having been described in general terms, a specific preferred embodiment will now be described.

The transmitter (in detail) Referring to Figure 9 of the drawings, a preferred embodiment of the transmitter is shown schematically.

The timing device 50 for the transmitter derives its timing pulses from a twin phantastron oscillator I00. This type of oscillator is noted for its linear behavior and constant timing. In the preferred embodiment, the components have such values that each half of the timing oscillator I runs down for 100 microseconds while the other half is recovering.

The timing oscillator is coupled to a scale-oftwo WI and a series of four pulse-forming stages I02, I03, I04 and I05. Each pulse-forming stage has an inductance in parallel with a rectifier in the cathode leg. Each inductance has a period selected to give a half-cycle wave form approximately microsecond long. The rectifier in shunt with the inductance prevents ringing, i. e., the combination of inductance and rectifier creates only a clear positive pulse. The output of one phase of the timing oscillator is taken off tube I06 and impressed on the grids of the tubes in pulse-forming stages I02 and I04. The output of the other phase of the timing oscillator is taken ofi tube I01 and impressed on the grids of the tubes in pulse-forming stages I 03 and W5. One output of timing oscillator tube I06 is taken off its cathode and impressed on the input of scale-of-two IIII. The output of tube I08 of the scale-of-two controls the gating bias on pulse-forming tubes I04 and IE5. The output of the other tube I09 of the scaleof-two controls the gating bias or" pulse-forming tubes I02 and 103. Thus the phases of signals from the timing oscillator and the scale-of-two are mixed in a different combination on each grid of the four separate pulse-forming tubes I02, I03, I04 and I05, thereby resulting in four evenly spaced pulses, each on a separate conductor. The sequence of pulses is indicated by the numerals I, 2, 3 or 4 adjacent the leads from the pulse-forming stages. of operation of the timer, in the preferred embodiment, a total of 10,000 equally spaced pulses are generated, of which 2500 per second appear on each output terminal.

In order to distinguish each signal channel from the other channels, each channel is initiated by a distinctive code of two pulses. The manner in which this is accomplished is now described. The assembly of component devices used for the purpose is termed the coder and is generally designated by numeral 5|.

A pulse from each of the pulse-forming stages I05, I04, I03 and I02 is impressed on amplifier stages, hereinafter termed coder stages, III, I I2, I I3 and H4, respectively.

The pulse from pulse generator stage I 05 is impressed on the input grid of the coder tube in stage III. One output is taken off the tapped anode load resistor of coder stage III at IIB. This output is impressed on manifold bus II! for direct use. A second output is taken oif the anode loa-d resistor of coder stage III at H8 and is impressed on manifold bus I I9 which is serially connected to delay line I20. The reason for tak- Thus, for each cycle ing the signal for the delay line circuit oil the coder tube load resistor at a point closer to the anode than the connection for the through manifold bus III is to obtain output pulses of equal magnitude on the mixed signal bus I2I. The delay line I20, in the present preferred embodiment, has a delay period of 3 microseconds. Consequently, from the single input pulse on coder stage I I I, two negative pulses of equal magnitude and spaced by 3 microseconds are obtained on the mixed signal bus I2I.

The next pulse, microseconds later, is generated by pulse-forming stage I04 and is impressed on coder stage H2. The output pulses are taken from the cathode leg of tube H5 and so are positive. The pulses of lower amplitude are connected by conductor I22 directly to manifold bus lead III and from there to mixed signal bus i2i. The pulse of higher amplitude passes to the mixed signal bus through delay line I28 and manifold bus H9. Therefore, two positive pulses spaced 3 microseconds apart appear on mixed signal bus I21 and constitute the second channel coding pair.

The third channel coding pair of pulses are obtained from pulse-forming stage I03 and coder stage I I3. The first pulse is taken from the anode and is negative. The second pulse is taken from the cathode and passes through delay line [23. Therefore, the third channel coding pair is a negative pulse followed 3 microseconds later by a positive pulse.

The fourth channel coding pair is obtained from pulse-forming stage Hi2 and coder stage I I I. The cathode pulse is led directly to the mixed signal line and the anode pulse is delayed. Therefore, the pair of pulses consist of a positive pulse followed in 3 microseconds by a negative pulse.

The sequence of channel coding pairs is impressed on one grid of two triodes in mixer stage 50. It is to be recalled that the coding pair establish the starting period for a duration to be terminated by the channel signal pulse.

The terminating channel signal pulse for channel I signal A is produced in modulator stage IA.

The observed signal voltage, whether D. C. or A. 0., or both is impressed on the terminals I23 and I24, respectively, of amplifier stage I25. The variation in potential at the anode of the tube of stage I25 is directly impressed on triode I28 connected to a phantastron delay generator comprising tube I2? and associated components. The phantastron is first triggered by the channel pulse I through conductor I28 running to pulse-forming stage I05. The square wave pulses generated by the screen of the phantastron have a length very closely determined by the conductivity of tube I26 in shunt with the anode load resistor of phantastron tube I2l. The conductivity of tube I263 is, in turn, determined by the input signal potential on input stage I255. From the foregoing, it is clear that phantastron I2! delivers a square Wave having a duration linearly determined within selected limits by the magnitude of the observed potential on input terminal I23. The trailing edge of the phantastron pulse is differentiated, rectified and connected to mixer input terminal I34 to impress negative pulses on mixer stage I29. Input terminal I34 and stage I2 are included in the mixer 56 to invert the trailing edge of the phantastron differentiated and rectified pulses when the light-emitted pulses are to be negative. A similar input modulator system is utilized for each signal to be handled. Therefore, in the embodiment shown, there are 11 three more input modulators for channel I, and a similar system of four input modulators similarly connected to each of pulse-forming stages I84, I83 and I82 for signals in channels II, III and IV.

The channel coding pulses and delayed signal pulses are mixed in mixer 56, then delivered to amplifier stage I33 though cathode follower I38, and impressed on light source I3I. The polarity of negative channel coding pulses and negative delayed signal pulse of channel I is reversed by tube I28 of mixer 55, and become positive pulses on the grid of tube I52 in stage I29. As a consequence, glow lamp I3I gives two channel coding positive intensity pulses and a delayed positive intensity pulse for channel I with signal IA.

The same techniques are extended so that three other delayed pulses, IB, IC and ID, follow signal IA in channel I. The system is similarly arranged ior channels II, III and IV so that the final signal takes the form of Figure 5.

The light emitter MI is a glow tube. A suitable commercial type is the Sylvania type R-l13lC. This tube is capable of transmitting both positive and negative changes in intensity of approximately 2 microseconds in duration.

The light beam is collimated by a lens and directed through one of the Van de Graaif high voltage insulating columns to fall on the lens of the light pulse receiver in the receiving system.

The receiver (in detail) A practical embodiment of the receiving system is shown in Figure 10. The light sensitive tube 2 1 is of the photomultiplier type. The pulses are taken off the ninth dynode in order to directly give the desired polarity of signal and are impressed on two-stage amplifier 8 I.

The output signal from the second stage is divided, one portion going directly into normal signal bus I58 and the other portion passed through 3 microsecond delay line I5I to delayed signal bus I52. The term normal means, like the original, that it is not delayed, inverted, or delayed inverted. The signals at this point on busses I58 and I52 are of original polarity. It is necessary to decode the four channel coding pairs into four distinct starting pulses corresponding to original codes I, II, III and IV. The normal signal bus I59 is coupled to the grids of tubes I53 and I5 5. Tube I5 l acts as an inverter and is coupled to tube I55. A normal set of signals is taken off the cathode of tube I53 and an inverted set of signals is taken off the cathode of tube I55.

The delayed signal bus I52 is coupled into the two-stage amplifier comprising tubes I58 and I57. A normal delayed set of signals and a delayed inverted set of signals are taken off the anode and cathode of tube I57, respectively. These sets of signals are shown in charts W, X, Y and Z, respectively, of Figure '7. These signals are applied in four different combinations to coincidence tubes I88, I8I, I82 and I83 in as many coincidence circuits.

The normal signal (as shown in chart W, Figure '7) is impressed on the first control grid of tubes I58 and I63. The normal inverted signal is impressed on the control grids of tubes IEI and I62. The delayed signal is impressed on the suppressor grids of tubes I58 and I82. The delayed inverted signals are impressed on the suppressor grids of coincidence tubes IGI and I83.

Referring again to Figure '7, it is noticed that the only coincidence between positive pulses derived from a normal set of signals and a delayed set of signals occurs between the channel code I second normal signal and the first of the code I delayed signals. Consequently, only coincidence tube I68 becomes conducting for the duration of one pulse width. The output pulse is denoted by 1'.

Tube IIiI is impressed with a set of delayed inverted pulses, and a set of inverted pulses. The only combination of coincidence between these sets of pulses shown in charts Y and Z of Figure 7 occurs for channel code pulse II.

A similar analysis of the circuit including 00- incidence tube I62 shows that channel code pulse III is decoded to give output starting pulse III. Similarly, coincidence tube I83 generates an output pulse IV corresponding to the fourth type of channel coding pulses.

It is apparent that both the signal pulses as well as the channel coding pulses are fed into the coincidence circuits, but the signal pulses are not used and do not cause trouble as long as the time sharing scheme of Figure 4 is observed. The signal pulses are the stop pulses for durations which are respectively correlated to transmitted quantities.

The useful signal or stop pulses are obtained from triodes I18, I'II, I12 and I13. These tubes are biassed below cut-01f and, consequently, are rendered conducting only by positive pulses. The control grids of tubes I18 and III are connected in parallel and to a source of normal Signal from the cathode of tube I53. The control grids of tubes I12 and I13 are impressed with a set of inverted signals from tube I55. Consequently, the original positive signal pulses A and C are obtained on separate leads from tubes I10 and II I, and the original negative pulses B and D are obtained on separate leads from tubes I12 and I13.

The decoded channel starting pulse corresponding to I is derived from coincidence tube I60 and is impressed on terminal I8I of flip-flop circuit I88 to fiip the same, and the stop pulse corresponding to the duration defined by original pulse I'A is impressed on terminal I82 to return the flip-flop circuit to its original state. The square wave so generated has a length determined by the interval between the pulse I and the signal pulse I'A'.

The square wave generated by flip-flop circuit I88 is impressed on sawtooth generator stage I85. The sawtooth generator is of the bootstrap variety and is of a type which is capable of large sweep amplitude and relative insensitivity to repetition frequency. Tube triode section I86 is utilized as a switch tube. Condenser I8! is directly in shunt with this tube. A charging resistor I88 is in series with switch tube I86 and condenser NW. A diode I88 in series with the charging resistor is utilized to supply an initial voltage at the supply end of resistor I89 at very nearly the supply potential.

Coupling condenser I98 connects between the cathode end of cathode resistor I92 and the grid of peak rectifier I85.

Operation of this circuit is as follows:

A negative pulse from flip-flop I88 open-circuits switch tube I86. The positive pulse from tube section I88 causes a sudden increase of current in tube section I9I and therefore in the cathode resistor I 92. The positive potential from cathode resistor I92 raises the potential of the cathode of diode I88 above the supply potential, thereby open-circuiting the diode. The total charging current into condenser I81 now flows from condenser I8Il. The potential across condenser I81 .phantastron tube IZI.

rises at a linear rate thereby increasing the current through tube section ISI at a linear rate and, consequently, generating a linear rise of potential across cathode resistor I92. This potential continues to rise until a positive pulse from the flip-flop on the grid of tube section I86 short circuits condenser I8! which, in turn, sharply reduces the current in cathode'resistor I92.

In order to obtain good linearity from the sawtooth generator, condenser ISO is large enough so that its potential does not appreciably drop during the period condenser I8! is being charged.

The wave form output from tube section I9! is shown in Figure 2, chart L. It is apparent that the peak voltage of the sawtooth wave form corresponds very closely to the duration between the start and stop pulses on the circuit input.

The sawtooth potential derived from sawtooth generator I85 is impressed on peak rectifier tube I95. The rectified potential is impressed on D. C. voltmeter I98.

M ultiplezm'ng The device of the present invention admits of the communication of several pieces of information on the time space allotted to one signal by a multiplexing operation. For example, a num ber of A. C. signals can be sent simultaneously in any channel so long as the peak-to-peak shift of the channel pulse does not exceed the permitted limits, and the frequencies do not exceed onehalf the repetition frequency. After detection, these frequencies can be separated by means of filters and utilized to energize relays or to perform other functions.

The multiplexing flexibility of the system herein disclosed also admits of several D. C. signals in any channel by utilization of a time sharing technique. An A. C. voltage is used to switch the phantastron modulator between two different D. C. inputs so that each input is effective approximately one-half the time. The switching is accomplished electronically and, in the preferred embodiment, at a 40-cycle per second rate. The output of such a channel after detection is electronically switched between two indications in synchronism with the switching input into the modulator. For this purpose, a IO-cycle per second signal is transmitted over the same link.

The manner in which such multiplexing is accomplished is shown in Figures 9, 10, 11 and 12.

Referring to Figure 9, modulator IA, it is seen that an A. C. potential can be impressed on modulator input stage I25 across ground and terminal i24 in addition to a D. C. potential across terminal I23 and ground. The variation in resistance of triode 126 in response to an A. C. input on stage I25 establishes an envelope for the sawtooth voltage generated by the screen coupled The voltages on the elements of a phantastron tube are shown in Figure 11. The turn-off of this circuit is determined by the bottoming of the plate voltage and it is seen that the screen voltage falls abruptly at this point. Consequently, the length of the rectangular pulse generated by the screen is determined by that voltage at which the plate bottoms. It follows that an A. C. voltage on the input of stage I25 determines the resistance of tube I 26 and therefore, the available voltage at the anode of phantastron tube I21. It follows that an A. C. variation of the anode voltage of the phantastron provides an envelope for the sawtooth voltage at the anode as shown in exaggerated form in Figure 12. This variation of the sawtooth peaks results in a sinusoidal variation in length of the sequence of screen rectangular voltages. This, when differentiated, gives a sinusoidal space time variation of generated pulses. It follows further that the simultaneous insertion of a D. C. and an A. C. signal voltage on the modulator input results in a mean delay corresponding to the D. C. input of the signal pulse from the channel coding pulse in the output of the mixer with a sinusoidally spaced time variation of the pulse at the A. C. rate and with a magnitude of the sinusoidal function which is proportional to the amplitude of the A. C. signal voltage. The combined transmitted channel coding pulses and the signal pulse for a combined A. C. and D. C. si nal in channel I is as shown in Figure 13.

At the receiver, Figure 10, the signal pulse varies the flop time of flip-flop 88 at the same sinusoidal variation about the mean time of delay which was determined by the D. C. signal voltage. The sawtooth voltage generated in sawtooth generator 485 therefore varies in the same manner as demonstrated in Figure 12 for the transmitter. The peak values are rectified in tube I and are averaged by the D. C. voltmeter I93. The sinusoidal variation in peak value is separated from the D. C. potential by series condenser 193 and is impressed on A. C. voltmeter I99. The filter I9? is anti-resonant to the repetition rate, i. e., in the preferred embodiment, to 2500 cycles per second.

It is apparent from the description, supra, that several A. C. potentials can be impressed simultaneously on the transmitter modulator and separated by tuned filters to give a plurality of corresponding A. C. instrument readings at the receiver.

In the event that only A. C. signals are transmitted over a signal channel, a simple sawtooth generator of the type shown in Figure 1A is satisfactory and takes the place oi the more complex sawtooth generator Ital shown in Figure 10 for duplex operation.

The manner in which several combinations of D. C. and A. C. signals can be transmitted in the time normally allotted to one signal is shown in Figure 15. The process for several D. C. signals is one of time sharing. Diagrammatically, it is shown in a manner explained supra, that a D. C. and an A. C. signal can share a signal channel. Two A. C. signals of different frequencies f1 and is can also simultaneously share the same signal channel.

By the use or" a synchronizing A. C. signal, two D. C. signals are transmitted in a time sharing scheme. The A. C. voltage is used to synchronize the transmitter and receiver so that the D. C. signal being received at any instant is directed to the instrument which is identified with the quantity selected to be measured in the transmitter.

Referring to Figure 15, the upper part of this figure shows how D. C. and A. C. signals are transmitted in single channels as explained supra. The lower part of this figure shows how two D. C. signals are alternately impressed on a time shared modulator 2%. A synchronizing A. C. wave is utilized to alternately switch the input of the modulator from one D. C. source to the other. The A. C. Wave is utilized both in its original form and in inverted form to accomplish the desired switching. Accordingl an A. C. inverter 2M is included in the transmitter assembly. The receiver assembly is similar to that of the transmitter in that a time shared detector 205 is associated with A. C. inverter 2 IE3. 

